Re: [PATCH] drm/i915/skl: Init cdclk in the driver rather than relying on pre-os

["Kumar, Shobhit" <shobhit.kumar@linux.intel.com>]

On 10/05/2015 09:05 PM, Imre Deak wrote:
> On ma, 2015-10-05 at 20:52 +0530, Shobhit Kumar wrote:
>> Mostly reuse what is programmed by pre-os, but in case there is no
>> pre-os initialization, init the cdclk with the default value.
>>
>> Cc: Imre Deak <imre.deak@intel.com>
>> Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_ddi.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
>> index 2d3cc82..675c60d 100644
>> --- a/drivers/gpu/drm/i915/intel_ddi.c
>> +++ b/drivers/gpu/drm/i915/intel_ddi.c
>> @@ -2947,10 +2947,8 @@ void intel_ddi_pll_init(struct drm_device *dev)
>>
>>   		cdclk_freq = dev_priv->display.get_display_clock_speed(dev);
>>   		dev_priv->skl_boot_cdclk = cdclk_freq;
>> -		if (!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE))
>> -			DRM_ERROR("LCPLL1 is disabled\n");
>> -		else
>> -			intel_display_power_get(dev_priv, POWER_DOMAIN_PLLS);
>> +
>> +		skl_init_cdclk(dev_priv);
>
> How does this prevent changing the clock if BIOS did enable some output?
> We shouldn't change the clock in that case.

In that case it will try to re-apply the same clock that BIOS enabled. 
Not sure if this is allowed, but I checked the cdclock change sequence 
and it is mostly followed in skl_init_cdclk. In my tests where BIOS does 
enable this, I faced no issues in initializing again in driver. I have 
noticed on some pre-os this value is programmed correctly except for the 
decimal part. That causes AUX transactions to fail on SKl. That is what 
triggered this patch actually. So other way is to completely validate 
the value in get_display_clock_speed instead of bit[28:26] and then if 
wrong then only do the cdclk init.

Regards
Shobhit

>
>>   	} else if (IS_BROXTON(dev)) {
>>   		broxton_init_cdclk(dev);
>>   		broxton_ddi_phy_init(dev);
>
>
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